Study On Community Structure And Function Of Ammonia-oxidizers And Denitrifiers In Different Habitats Of Lake Taihu

The biogeochemical cycle of nitrogen in the aquatic environment is the research hotspot in the world all the time.Microorganisms are considered the main drivers of the nitrogen cycle.Nitrification and denitrification are the special processes of the microorganism,and also the key steps in the nitrogen biogeochemical cycle possessing great significance in the freshwater ecosystem.Aquatic macrophytes in freshwater ecosystems are of significance in the repair process of the eutrophic water.Understanding the effect of aquatic macrophytes on dynamics of ammonia oxidizers and denitrifiers is of significant importance.Nevertheless,little was known in this term.Cyanobacterial bloom caused drastic changes in terms of concentration and transformation of nitrogen in freshwater lake ecosystems.However,the current studies of algal blooms in freshwater lake ecosystems mainly focus on changes of bacterial communities based on 16s rDNA,the community dynamics of the nitrogen cycling microorganisms is still unknown.In this study,the abundance and/or communities dynamics of ammonia oxidizers as well as denitrifiers in the sediments of areas suffering algae blooms was examined in Lake Taihu sediments through field investigation.Moreover,the mesocosm experiments with varying levels of algal biomass in the freshwater water column to study the effect of algae blooms on ammonia oxidizers and denitrifiers.Meanwhile,the influence of submersed macrophytes and floating macrophytes to the ammonia oxidizers and denitrifiers were investigated in sediment and water,respectively.The results showed as following:1)The concentrations of ammonium,dissolved organic carbon(DOC)and pH affected the ammonia oxidizers most in sediment due to algal bloom and subsequently.Sediment with high level of nitrogen and phosphorus nutrient harbored abundant AOA and AOB diversity.However,the sediment with higher total dissolved nitrogen and ammonium content was not conducive to the AOA amoA abundance.On the contrary,lower ammonium concentration in the sediment favored AOA.Sediment with higher levels of dissolved inorganic nitrogen and deeper oxygen erosion depth was more prone to the coupled nitrification-denitrification.AOA community structure in the sediments with aquatic vegetation was more stable.Ammonia oxidation in this type of sediment was driven by AOA.However,the presence of aquatic macrophytes was not conducive to the proliferation of denitrifying microorganisms with nir gene.Nitrosomonas adapts to sediments of various types;while Nitrosospira favored sediment of lower ammonium content and pH value.2)The results that simulation of repeated outbreaks of cyanobacterial blooms using micro-universe system in lab showed that the denitrification in the water was promoted by cyanobacterial bloom;and the amoA gene abundance was reduced in the early stage of it.In the processes of repeated outbreaks of cyanobacterial blooms,chlorophyll a,dissolved oxygen,pH,dissolved organic carbon,total nitrogen,ammonium nitrogen and phosphate trends were reproducible.And the bacterial community composition in the water also showed a certain degree of reproducibility within the first 2 days.Therefore,the bacterial communities resistance to cyanobacteria bloom disturbance was not reduced but the restoring force of bacterial communities was reduced after repeated outbreaks of blooms.3)It was found during the mesocosm study that Vallisneria natans helped to increase the abundance and biodiversity of AOA in both sediments of East Lake Taihu and Meiliang Bay.Presence of Vallisneria natanswas conducive to the AOB biodiversity in the East Lake Taihu sediment;however,Vallisneria natans had no significant effect on AOB amoA gene abundance in both types of sediment.Compared with Nitrosospira,Nitrosomonas dominated AOB community in this study.Presence of Vallisneria natans conducive to Nitrosospira.The ammonia oxidation in sediments of both types with Vallisneria natans was driven by AOA.4)It was found during the mesocosm study that AOA and AOB amoA gene copies were promoted by Eichhornia crassipes rhizosphere,the contribution of which was not related to the biofilm colonization on the surface of roots.The presence of Eichhornia crassipes did not favor the increase of nirK and nirS abundance in water column.The presence of Eichhornia crassipes helped to raise the activity of Nitrosomonas europaea lineage and Nitrospira as well as metabolism of Nitrospira.